Conventionally, optical components, such as an optical lens and a prism, are used for optical apparatuses, such as a camera, a microscope, and a telescope, recording devices of an electrophotography system, such as a printer, and a copying apparatus, optical recording devices such as a DVD, and optical devices for communications and industries. Although focal lengths of usual optical lenses are fixed, some of the above-mentioned apparatuses and devices may use lenses whose focal lengths can be adjusted according to circumstances, i.e., so-called variable-focal length lenses. The conventional variable-focal length lens adjusts its focal length mechanically with a combination of a plurality of lenses. However, there was a limit in such a mechanical variable-focal length lens in extending its application range in terms of a response speed, manufacture costs, miniaturization, power consumption, etc.
Then, there have been devised a variable-focal length lens such that a material whose refractive index is variable is applied to a transparent medium that makes up an optical lens, variable-focal length lens whose shape of the optical lens is mechanically deformed, not moving a position of the optical lens, etc. As a former variable-focal length lens, the variable-focal length lens that uses a liquid crystal is proposed as an optical lens. This variable focal length lens confines a liquid crystal in a container made of a transparent material by sandwiching the liquid crystal with two glass plates or other ways. Because the inner side of this container is processed to be a spherical surface, the liquid crystal is formed in a lens shape and becomes a variable-focal length lens. Transparent electrodes are provided on the inside of this container. By applying an electric field to the liquid crystal, its refractive index is controlled, and a focal length invariably controlled (e.g., refer to Patent Document 1).
For the latter variable-focal length lens, a liquid is used in many cases as a material of a deforming lens. For example, the variable-focal length lens described in Nonpatent Document 1 has a structure that encloses a liquid, such as silicone oil, in a space sandwiched by glass plates. The glass plates are processed thin, and the lens constructed with oil and the whole glass plates is deformed by putting a pressure on the glass plates externally with a lead zirconate titanate (PZT) piezo actuator, and thereby a focusing position is controlled. An operating principal of this variable focal length lens is the same as that of the crystalline lens of the eyeball.
However, the conventional variable-focal length lenses, in any one of the variable-focal length lens that mechanically adjusts its focal length, the variable-focal length lens that controls the refractive index by applying an electric field to a liquid crystal, and variable-focal length lens that deforms a lens by a PZT piezo actuator, have a problem that there is a limit in response speed needed to alter their focal lengths, and thereby each is inapplicable to a high-speed response of 1 ms or less.
The object of the present invention is to provide a variable-focal length lens capable of altering its focal length at high speed.
[Patent Citation 1] Japanese Patent Laid-open No. H11-64817 (1999)
[Non patent Citation 1] Takuya KANEKO, “Optical Microscope Expanded Depth of Field using Dynamic Focusing Lens for Micro Parts Assembling”, Denso Technical Review, Vol. 3, No. 1, pp. 52-58, 1998.